The amount of data and information routinely transmitted on a world-wide basis over the world's existing 1.2 billion telephones and associated telephone lines continues to increase. Digital and analog data transmitted over telephone lines is often generated through modems and received by other modems, without at any time exhibiting an acoustic characteristic (i.e. an audible signal) at any time. In addition, data and information which is voice coupling based, for example normal conversation, has an acoustic characteristic. Data and information having an acoustic characteristic continues to constitute a substantial portion of the information sent over telephone lines. This information has the characteristic of being acoustic at at least some point before being converted, through the use of transducers such as microphones, into electromagnetic signals and transmitted over physical lines (e.g. optical fibers, cables, wires, and the like) or, alternatively, transmitted via stations such as satellites as electromagnetic waves.
With regard to voice coupled or acoustic information, it is known that the digital information is transmitted as acoustic waves at least for a portion of its path, for example from the sound generator to the sound transducer (e.g. microphone) which resides in a typical telephone mouthpiece.
One know prior art application of acoustic coupling involves a modem device used as an acoustic coupling device, such as an acoustic coupling cradle for receiving a telephone headset in intimate physical contact with the acoustic coupling device. This method of acoustic coupling of the telephone headset with the telephone line has largely been replaced with the technique of electrically connecting the modem directly to the telephone lines, thus substantially increasing the rate of transmission of information.
A further known example of acoustic coupling involves the well-known Dual Tone Multi-Frequency (DTMF) scheme. In the most popular DTMF scheme, digital information is transmitted as voice coupled (acoustic) information. In a typical DTMF system a person presses a button on a telephone keypad, where upon two phenomena occur. In the first instance, a characteristic sound associated with the depressed button is generated and played through the telephone headset such that it is audible to the user. In addition, an electrical signal associated with the depressed key is generated for transmission by the telephone to a desired destination. Thus, the term "DTMF" encompasses both an electrical magnetic DTMF and an acoustic DTMF.
Other devices are generally known which generate DTMF tones, but which are separate from the telephone. For example, DTMF generating modules are known which generate tones as an acoustic wave outside the phone, for example by a Tone Dialer. The acoustic wave generated by the Tone Dialer may be picked up by the telephone headset microphone and transmitted through the telephone to a desired destination.
A popular use of DTMF devices involves their use with Interactive Voice Response (IVR) boards, for example through the use of DTMF tones to chose a particular item from a verbal menu. That is, when a caller desires to interact with an IVR system, the caller dials up a telephone line associated with the IVR computer through the use of a conventional telephone. The IVR board associated with the central computer generates human audible voice commands, and prompts the caller to select various menu options through the use of DTMF tones.
The acoustic DTMF tone may be characterized as a sound associated with a particular button pressed by the caller. This is true whether the caller employs the Keypad on the telephone to generate DTMF tones or, alternatively, if the caller uses a separate DTMF or tone dialing module to generate the DTMF tones. In either case, the sound is typically composed of two frequency components: a first frequency selected out of a group of four "low" frequencies, and a second frequency selected from a group of four "high" frequencies. This two frequency tone is picked up by the microphone in the telephone headset, and eventually converted into an electrical signal (the electromagnetic DTMF). This signal then travels through the phone lines until it reaches its destination, carrying the digital information encoded as an analog electromagnetic wave. The IVR board detects the signal through the use of an array of hardware and/or software filters. When the IVR board processes the signal and identifies the particular DTMF tone, it informs the computer associated with the IVR board of the particular "button" depressed by the caller, for example one of the numbers 0-9 or the characters "*" and "#".
Another popular use of voice coupled information surrounds the dialing function employed by telephone networks having a Central Office which is DTMF capable but for which at least some of the telephones associated with the telephone network are not DTMF capable. More particularly, in the case of "non-touch tone telephones" (also referred to as "rotary" or "pulse" telephones), a DTMF tone dialer may be employed by the user of a non-DTMF telephone to acousticly generate DTMF tones in order to dial a number or otherwise communicate with a DTMF-based destination. The acoustic DTMF signal generated by the tone dialer is picked by the transducer at the telephone, and converted into a DTMF electromagnetic signal and thereafter transmitted by the telephone.
Other uses and applications of acoustic coupling techniques are set forth in Patent Cooperation Treaty (PCT) application serial no. PCT/US92/10492, the entire disclosure of which is hereby incorporated by this reference. For example, acoustic coupling devices may be used in the context of over-the-phone identification systems based on the use of special tone dialers which generate a string of acoustic DTMF signals representative of credit card transaction data, digital signatures, and other data and information.
Theoretically, digital information may be transmitted over telephone lines by associating a different frequency with the various digital characters sought to be transmitted, much in the nature of a conversion table. Such a table would theoretically assign to each alphanumeric character a unique frequency. In this way, each time a sound wave corresponding to particular frequency is applied to the telephone transducer, it would be converted into an electrical signal representative of that same frequency and transmitted. When the signal is detected at the destination, the respective alphanumeric character corresponding to that particular frequency would be detected by the destination. While perhaps viable theoretically, this approach is problematic in several respects.
For example, electrical and acoustic noises are inevitably present in the background, transmission hardware, and other aspects of the transmission system. Consequently, the detection filters will inevitably detect spurious frequency activity.
To reduce the incidence of spurious noise in the context of DTMF systems, the existing DTMF paradigm has evolved with a first set of low frequencies (e.g. 697 Hz, 770 Hz, 852 Hz, and 941 Hz) and a second set of high frequencies (e.g. 1209 Hz, 1336 Hz, 1447 Hz, and 1663 Hz). By requiring the detection of one frequency from the low frequency group simultaneously with one frequency from the high frequency group, wherein both frequencies are required to exceed a minimum amplitude threshold, a substantial amount of spurious background noise may be eliminated. Nevertheless, existing DTMF systems remain susceptible to the detection of false DTMF signals and the non-detection of true DTMF signals.
A further problem associated with existing DTMF signals surrounds the fact that transmission line quality can vary from call to call, even when using the same telephone, as well as the fact that noise may be generated at virtually any stage during transmission. Finally, such factors as absorption and gain along the transmission lines affect different frequencies to different degrees. In order to overcome some of these difficulties, existing DTMF systems may require a specific range of amplitude for respective activities, i.e. a minimal amplitude.
A further problem associated with acoustic coupling systems involve the frequency response characteristic of the telephone mouth piece transducer (e.g. microphone). In particular, the transmission of data using sound waves, in particular acoustic DTMF signals, may be adversely affected by the transducers frequency response characteristic, and thus may impact the accuracy with which acoustic signals are converted into electrical signals. Moreover, the frequency response characteristics vary from telephone to telephone; the frequency response characteristic for a particular telephone may even change with the physical position of the microphone in respect of the local vertical or gravitational line.
Yet a further problem associated with existing DTMF voice coupling systems surrounds the elapsed transmission time typically required for a DTMF tone transmission. More particularly, as a result of the fact that a plurality of filters are often needed to effectively receive and identify a DTMF tone, a particular tone must be generated on the order of a minimum of at least 40 milliseconds in duration; 75 milliseconds per tone is more common. In addition, a "pause" generally on the order of 40 milliseconds is often used as a separation window between tones. Consequently, the transmission of on the order of 100 hexadigits may last 11.5 seconds or more; this is typically cumbersome and simply requires more time than is practical for the transmission of large volumes of data quickly and efficiently.
A system and method is thus needed which overcomes the acoustic transmission and acoustic coupling problems associated with existing DTMF transmission systems.